Study Finds Male Infants at Increased Risk for NAS

Male infants are more likely at birth than their female counterparts to be diagnosed with drug withdrawal symptoms, also known as neonatal abstinence syndrome (NAS), and to require treatment, according to a new Vanderbilt study published in Hospital Pediatrics.

The retrospective cohort study used vital statistics and prescription, outpatient and inpatient data for mothers and infants enrolled in the Tennessee Medicaid program between 2009 and 2011. Of the 102,695 mother-infant pairs enrolled, 484 male subjects and 443 female infants were diagnosed with NAS.

The Vanderbilt researchers’ findings revealed that male infants were 18 percent more likely than female infants to be diagnosed with NAS and 24 percent more likely to require pharmacologic treatment for the syndrome. The study represents the largest reported cohort to date investigating sex-related differences in incidence and severity of NAS.

“As pediatricians, we know that not every newborn exposed to opioids develops NAS, but we don’t know why. In our analysis of a large population of opioid-exposed infants, we found that male infants were more likely to be diagnosed with NAS than female infants,” said senior author

Neonatal abstinence syndrome has been linked to both illicit drug use as well as the use of prescription opioids — narcotic pain relievers such as hydrocodone — by pregnant women. Infants born with NAS are more likely to have respiratory complications, feeding difficulty, jaundice, seizures and low birth weight.

Researchers in this latest study found that male infants with NAS were diagnosed with associated respiratory difficulties more frequently, but were not more likely than female infants to be diagnosed with other associated clinical complications of the syndrome. Male infants also had length of stays in the hospital similar to females, and severity of an NAS diagnosis was the same among both groups.

The researchers say that while no unifying theories exist to explain male infants’ susceptibility to NAS, many hypotheses consider differences in neurologic development. Males tend to require a longer neurologic maturation period and therefore are more vulnerable.

“Our team’s previous work found that the number of infants with NAS grew nearly fivefold nationwide over the last decade. Pediatricians today are far more likely to care for an opioid-exposed infant than they were just a few years ago; however, there are few tools to guide treatment. This study is one step forward in tailoring treatment for opioid-exposed infants more precisely,” said Patrick.